Here is what happened: Having never been to Winterhold before, I needed to go there to do the Forbidden Legend quest which had the dungeon Saalthar nearby. I took a wagon and upon arrival headed Southwest, and saw a dragon flying overhead. Not wanting to deal with it, I sprinted to Saalthar and forgot it. Later, I fast traveled back to Winterhold. The last dragon was still there, and random dragon spawning added a fellow dragon.

They both died at the same spot. My Nord woman poisoner must have creamed herself from the double MacLeod dragon quickening.